for Submariners

by Hamilton 1:1 Communications, LLC

Greater Underwater Propulsion Power Program
Guppy I

If you wish to use this image for the back of your Business Card or another product, please simply type it's name and hull number in the appropriate text field on the options list found on the product page in the shopping section. To be redirect to the shopping section home page click on "Shop Now" in the menu bar.

Greater Underwater Propulsion Power Program (GUPPY)

The United States Navy initiated this program after World War II to improve the submerged speed, maneuverability, and endurance of its submarines.

The Navy began the program by testing and reverse engineering two captured Type XXI U-Boats; U-2513 and U-3008. That analysis led to four goals: increasing the submarines' battery capacity, streamlining the boats' structures, adding snorkels, and improving fire control systems. The Navy immediately focused on designing a new class of submarines, but the Bureau of Ships believed that the vast fleet of existing Gato, Balao and Tench class submarines could be modified to incorporate the desired improvements. In June 1946, the Chief of Naval Operations approved the GUPPY project. The initial two-boat test program, implemented by the Portsmouth Naval Shipyard, eventually grew into several successive conversion programs. Those upgrades preceded in seven variants GUPPY I, GUPPY II, GUPPY IA, Fleet Snorkel, GUPPY IIA, GUPPY IB, and GUPPY III. (The apparently out-of-order sequence is correct; see below.) Some boats that went through an early phase were then upgraded further in a later phase.


The prototype GUPPYs, Odax and Pomodon (both Portsmouth-built Tench boats), appeared in 1947. Externally, they featured improved streamlining of the bridge and shears structures, and periscope and radar  supports. To reduce hydrodynamic drag, one of the periscopes was deleted. No snorkel was fitted, due to difficulties in adapting the snorkel to the fleet boat. Deck guns and their associated containers were removed. An SV radar aerial was added to the top of the sail, creating a distinctive side bulge. All capstans, cleats, and rail stanchion supports were redesigned so they could be retracted or removed when rigged for dive. Most notably, the sharp V-shaped "fleet boat bow" was replaced with a distinctive rounded "Guppy bow" that improved submerged performance.

These modifications changed not only the boats themselves but also their terminology: after a GUPPY conversion, the faired structure around the boat's conning tower and mast supports was called the "sail."

Internally, the boats underwent considerable rearrangement to accommodate larger battery wells and batteries of greatly increased electrical power. The batteries themselves were of a new design. Compared with the original Sargo battery, the Guppy battery used a greater number of thinner plates that would generate higher current for a longer time. However, these batteries had a shorter life, 18 months versus the five years of the Sargo battery, and took longer to charge. They also required ventilation to remove hydrogen gas, and required cooling water to the battery terminals and termination bars. Four 126-cell batteries were installed in enlarged battery wells that replaced former storage, ammunition, and refrigeration spaces. These four batteries could be connected in series or parallel, providing a wide range of voltages and currents, and thus a wide range of speeds.

In the maneuvering room, two or four of the earlier high-speed motors and reduction gears were replaced by slow-speed motors. All open-front switchboards were replaced with enclosed splash-proof cabinets. Lighting and other "hotel" electrical loads were converted to use 120 volt 60 hertz alternating current, and ship electronics to use 120 volt 400 hertz AC. A new air conditioning system of greatly increased capacity was also installed.

In service, these boats offered massively improved underwater performance. USS Pomodon reached 17.8 knots (km/h) surfaced and 18.2 knots (33.7 km/h) submerged, USS Odax slightly less.




307' 7" length
27' 4” Beam
17' Draft
1,570 tons Surfaced Displacement
2,400 tons Submerged Displacement
4,610 SHP Diesels, 2 Shafts
4,610 SHP Electric Motors, 2 Shafts
17.8 kt surfaced speed
18.2 kt submerged speed
400 ft Test Depth


6 x 21” TT Bow
4 x 21” TT Stern
22 x 21” Torpedoes